1. Field of the Invention
This invention relates to a control apparatus for an automatic clutch mounted on a vehicle, and more particularly to an apparatus for protecting the automatic clutch from overheating.
2. Description of the Related Art
In order to engage a clutch when starting an automatic-clutch-mounted vehicle, the clutch is controlled so that a smooth engagement thereof can be attained, by gradually increasing transmission torque of the clutch in accordance with a rotational speed of an internal combustion engine and a vehicle speed. During this time, a semi-clutch-engaged condition is necessarily continued as a clutch engaging force is increased from an engagement starting time to an engagement completion time. In this semi-clutch-engaged condition, the clutch is in a slipping state, so that heat is generated greatly. When a traveling load at a vehicle starting time is large, the semi-clutch-engaged condition continuation time increases, and this causes the burning of the clutch in some cases. In order to prevent such burning of a clutch, various kinds of measures are taken. For example, the techniques disclosed in Japanese Laid-Open Patent No. 89795/1994 constitute an example of these measures.
According to the techniques disclosed in this publication, a judgement that a traveling load is large is given when not shorter than a predetermined period of time has elapsed after the arrival of the time at which a vehicle started at such a level of rotational frequency of an internal combustion engine that is in the vicinity of a stall point is to reach a set vehicle speed, and a signal the level of which corresponds to the length of the mentioned time elapsed is outputted so as to increase in a current setting unit of an electromagnetic clutch the gradient of the rising characteristics of a clutch current with respect to a rotational speed of the internal combustion engine. Namely, when a traveling load is judged large, the engagement of the clutch is effected earlier by hastening the increasing of a clutch current, and a slipping period is thereby shortened. This prevents the heat from doing damage to the clutch.
Thus, in a related art clutch, the measures for preventing the burning of the same by hastening the engagement thereof are taken. Such techniques are effective when the weight onboard is increased, and when a vehicle runs up a slope. However, an increase in a traveling load is encountered not only in such a case. Such a load increase also occurs when a parking brake is not disengaged, and when the starting of a vehicle is prevented by objects of a larger height, such as a vehicle stops which the vehicle cannot get over. When the above-mentioned system having a function of protecting a vehicle from overheating is put in operation in such cases, the clutch is controlled so that it is forcibly engaged. This causes brakes to be overheated, the momentary overheating of the clutch to occur, or a shock and an engine failure to occur.
The present invention has been made in view of the above-mentioned circumstances, and provides an apparatus for protecting an automatic clutch from overheating, capable of holding down the heating of the clutch by minimizing an output from an internal combustion engine when a traveling load exceeds a predetermined level with this excessive load condition continuing for a predetermined period of time, and thereby returning the operation of the engine to a normal condition without stopping the engine.
According to an aspect of the present invention, the apparatus for protecting an automatic clutch from overheating, wherein the automatic clutch is provided in a power transmission path between an internal combustion engine mounted on a vehicle and a transmission adapted to change a speed represented by an output from the engine, the apparatus comprising:
a pressure sensor adapted to detect a pressure in an intake manifold of the internal combustion engine,
a degree of opening of accelerator sensor adapted to detect an operation amount of an accelerator,
a vehicle speed sensor adapted to detect a traveling speed of a vehicle, and
a control unit adapted to detect a traveling load of the vehicle at a vehicle starting time on the basis of the outputs of the pressure sensor, the degree of opening of accelerator sensor, and the vehicle speed sensor, and to control a throttle actuator by which a throttle valve provided in the intake manifold of the internal combustion engine is operated,
wherein the control unit being adapted to control the throttle valve so that the throttle valve is moved to and closed in a position of a preset level when the traveling load is not lower than a predetermined level with the vehicle speed continuing to be not higher than a predetermined value for a period of time not shorter than a predetermined period of time, and thereby protect the automatic clutch.
On the basis of such a structure, the throttle valve is closed in a predetermined period of time even when a vehicle is tried to be started in a case where the starting of the vehicle is hindered by an unreleased parking brake or a block which the vehicle cannot get over. This enables the generation of heat ascribed to the continuation of a slipping condition of the automatic clutch to be held down, and the burning of the clutch to be prevented.
According to another aspect of the present invention, the apparatus for protecting an automatic clutch from overheating, wherein, when the condition in which the traveling load is not lower than the predetermined level and the vehicle speed is not higher than the predetermined value continues for the predetermined period of time, the control unit operates the throttle valve being closed so that an internal combustion engine attains an idling rotational speed, and the automatic clutch thereby release to disconnect the internal combustion engine and the transmission.
On the basis of such a structure, the generation of heat in and the burning of the automatic clutch can be prevented, and a subsequent operation can be carried out without accompanying an engine stall.
According to still another aspect of the present invention, the apparatus for protecting an automatic clutch from overheating, wherein an electromagnetic powder clutch is used as the automatic clutch.
On the basis of such a structure, the above-mentioned operation for protecting the clutch from heating can be carried out with a high accuracy by simple electric circuit and program.